// Copyright 2012-2016 The Rust Project Developers. See the COPYRIGHT // file at the top-level directory of this distribution and at // http://rust-lang.org/COPYRIGHT. // // Licensed under the Apache License, Version 2.0 or the MIT license // , at your // option. This file may not be copied, modified, or distributed // except according to those terms. use self::Constructor::*; use self::Usefulness::*; use self::WitnessPreference::*; use rustc::dep_graph::DepNode; use rustc::middle::const_val::ConstVal; use ::{eval_const_expr, eval_const_expr_partial, compare_const_vals}; use ::{const_expr_to_pat, lookup_const_by_id}; use ::EvalHint::ExprTypeChecked; use rustc::hir::def::*; use rustc::hir::def_id::{DefId}; use rustc::middle::expr_use_visitor::{ConsumeMode, Delegate, ExprUseVisitor}; use rustc::middle::expr_use_visitor::{LoanCause, MutateMode}; use rustc::middle::expr_use_visitor as euv; use rustc::middle::mem_categorization::{cmt}; use rustc::hir::pat_util::*; use rustc::traits::ProjectionMode; use rustc::ty::*; use rustc::ty; use std::cmp::Ordering; use std::fmt; use std::iter::{FromIterator, IntoIterator, repeat}; use rustc::hir; use rustc::hir::{Pat, PatKind}; use rustc::hir::intravisit::{self, IdVisitor, IdVisitingOperation, Visitor, FnKind}; use rustc_back::slice; use syntax::ast::{self, DUMMY_NODE_ID, NodeId}; use syntax::codemap::{Span, Spanned, DUMMY_SP}; use rustc::hir::fold::{Folder, noop_fold_pat}; use rustc::hir::print::pat_to_string; use syntax::ptr::P; use rustc::util::nodemap::FnvHashMap; pub const DUMMY_WILD_PAT: &'static Pat = &Pat { id: DUMMY_NODE_ID, node: PatKind::Wild, span: DUMMY_SP }; struct Matrix<'a>(Vec>); /// Pretty-printer for matrices of patterns, example: /// ++++++++++++++++++++++++++ /// + _ + [] + /// ++++++++++++++++++++++++++ /// + true + [First] + /// ++++++++++++++++++++++++++ /// + true + [Second(true)] + /// ++++++++++++++++++++++++++ /// + false + [_] + /// ++++++++++++++++++++++++++ /// + _ + [_, _, ..tail] + /// ++++++++++++++++++++++++++ impl<'a> fmt::Debug for Matrix<'a> { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { write!(f, "\n")?; let &Matrix(ref m) = self; let pretty_printed_matrix: Vec> = m.iter().map(|row| { row.iter() .map(|&pat| pat_to_string(&pat)) .collect::>() }).collect(); let column_count = m.iter().map(|row| row.len()).max().unwrap_or(0); assert!(m.iter().all(|row| row.len() == column_count)); let column_widths: Vec = (0..column_count).map(|col| { pretty_printed_matrix.iter().map(|row| row[col].len()).max().unwrap_or(0) }).collect(); let total_width = column_widths.iter().cloned().sum::() + column_count * 3 + 1; let br = repeat('+').take(total_width).collect::(); write!(f, "{}\n", br)?; for row in pretty_printed_matrix { write!(f, "+")?; for (column, pat_str) in row.into_iter().enumerate() { write!(f, " ")?; write!(f, "{:1$}", pat_str, column_widths[column])?; write!(f, " +")?; } write!(f, "\n")?; write!(f, "{}\n", br)?; } Ok(()) } } impl<'a> FromIterator> for Matrix<'a> { fn from_iter>>(iter: T) -> Matrix<'a> { Matrix(iter.into_iter().collect()) } } //NOTE: appears to be the only place other then InferCtxt to contain a ParamEnv pub struct MatchCheckCtxt<'a, 'tcx: 'a> { pub tcx: TyCtxt<'a, 'tcx, 'tcx>, pub param_env: ParameterEnvironment<'tcx>, } #[derive(Clone, PartialEq)] pub enum Constructor { /// The constructor of all patterns that don't vary by constructor, /// e.g. struct patterns and fixed-length arrays. Single, /// Enum variants. Variant(DefId), /// Literal values. ConstantValue(ConstVal), /// Ranges of literal values (2..5). ConstantRange(ConstVal, ConstVal), /// Array patterns of length n. Slice(usize), /// Array patterns with a subslice. SliceWithSubslice(usize, usize) } #[derive(Clone, PartialEq)] enum Usefulness { Useful, UsefulWithWitness(Vec>), NotUseful } #[derive(Copy, Clone)] enum WitnessPreference { ConstructWitness, LeaveOutWitness } impl<'a, 'tcx, 'v> Visitor<'v> for MatchCheckCtxt<'a, 'tcx> { fn visit_expr(&mut self, ex: &hir::Expr) { check_expr(self, ex); } fn visit_local(&mut self, l: &hir::Local) { check_local(self, l); } fn visit_fn(&mut self, fk: FnKind<'v>, fd: &'v hir::FnDecl, b: &'v hir::Block, s: Span, n: NodeId) { check_fn(self, fk, fd, b, s, n); } } pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) { tcx.visit_all_items_in_krate(DepNode::MatchCheck, &mut MatchCheckCtxt { tcx: tcx, param_env: tcx.empty_parameter_environment(), }); tcx.sess.abort_if_errors(); } fn check_expr(cx: &mut MatchCheckCtxt, ex: &hir::Expr) { intravisit::walk_expr(cx, ex); match ex.node { hir::ExprMatch(ref scrut, ref arms, source) => { for arm in arms { // First, check legality of move bindings. check_legality_of_move_bindings(cx, arm.guard.is_some(), &arm.pats); // Second, if there is a guard on each arm, make sure it isn't // assigning or borrowing anything mutably. match arm.guard { Some(ref guard) => check_for_mutation_in_guard(cx, &guard), None => {} } } let mut static_inliner = StaticInliner::new(cx.tcx, None); let inlined_arms = arms.iter().map(|arm| { (arm.pats.iter().map(|pat| { static_inliner.fold_pat((*pat).clone()) }).collect(), arm.guard.as_ref().map(|e| &**e)) }).collect::>, Option<&hir::Expr>)>>(); // Bail out early if inlining failed. if static_inliner.failed { return; } for pat in inlined_arms .iter() .flat_map(|&(ref pats, _)| pats) { // Third, check legality of move bindings. check_legality_of_bindings_in_at_patterns(cx, &pat); // Fourth, check if there are any references to NaN that we should warn about. check_for_static_nan(cx, &pat); // Fifth, check if for any of the patterns that match an enumerated type // are bindings with the same name as one of the variants of said type. check_for_bindings_named_the_same_as_variants(cx, &pat); } // Fourth, check for unreachable arms. check_arms(cx, &inlined_arms[..], source); // Finally, check if the whole match expression is exhaustive. // Check for empty enum, because is_useful only works on inhabited types. let pat_ty = cx.tcx.node_id_to_type(scrut.id); if inlined_arms.is_empty() { if !pat_ty.is_empty(cx.tcx) { // We know the type is inhabited, so this must be wrong let mut err = struct_span_err!(cx.tcx.sess, ex.span, E0002, "non-exhaustive patterns: type {} is non-empty", pat_ty); span_help!(&mut err, ex.span, "Please ensure that all possible cases are being handled; \ possibly adding wildcards or more match arms."); err.emit(); } // If the type *is* empty, it's vacuously exhaustive return; } let matrix: Matrix = inlined_arms .iter() .filter(|&&(_, guard)| guard.is_none()) .flat_map(|arm| &arm.0) .map(|pat| vec![&**pat]) .collect(); check_exhaustive(cx, ex.span, &matrix, source); }, _ => () } } fn check_for_bindings_named_the_same_as_variants(cx: &MatchCheckCtxt, pat: &Pat) { pat.walk(|p| { if let PatKind::Binding(hir::BindByValue(hir::MutImmutable), name, None) = p.node { let pat_ty = cx.tcx.pat_ty(p); if let ty::TyEnum(edef, _) = pat_ty.sty { let def = cx.tcx.def_map.borrow().get(&p.id).map(|d| d.full_def()); if let Some(Def::Local(..)) = def { if edef.variants.iter().any(|variant| variant.name == name.node.unhygienize() && variant.kind() == VariantKind::Unit ) { let ty_path = cx.tcx.item_path_str(edef.did); let mut err = struct_span_warn!(cx.tcx.sess, p.span, E0170, "pattern binding `{}` is named the same as one \ of the variants of the type `{}`", name.node, ty_path); help!(err, "if you meant to match on a variant, \ consider making the path in the pattern qualified: `{}::{}`", ty_path, name.node); err.emit(); } } } } true }); } // Check that we do not match against a static NaN (#6804) fn check_for_static_nan(cx: &MatchCheckCtxt, pat: &Pat) { pat.walk(|p| { if let PatKind::Lit(ref expr) = p.node { match eval_const_expr_partial(cx.tcx, &expr, ExprTypeChecked, None) { Ok(ConstVal::Float(f)) if f.is_nan() => { span_warn!(cx.tcx.sess, p.span, E0003, "unmatchable NaN in pattern, \ use the is_nan method in a guard instead"); } Ok(_) => {} Err(err) => { let mut diag = struct_span_err!(cx.tcx.sess, err.span, E0471, "constant evaluation error: {}", err.description()); if !p.span.contains(err.span) { diag.span_note(p.span, "in pattern here"); } diag.emit(); } } } true }); } // Check for unreachable patterns fn check_arms(cx: &MatchCheckCtxt, arms: &[(Vec>, Option<&hir::Expr>)], source: hir::MatchSource) { let mut seen = Matrix(vec![]); let mut printed_if_let_err = false; for &(ref pats, guard) in arms { for pat in pats { let v = vec![&**pat]; match is_useful(cx, &seen, &v[..], LeaveOutWitness) { NotUseful => { match source { hir::MatchSource::IfLetDesugar { .. } => { if printed_if_let_err { // we already printed an irrefutable if-let pattern error. // We don't want two, that's just confusing. } else { // find the first arm pattern so we can use its span let &(ref first_arm_pats, _) = &arms[0]; let first_pat = &first_arm_pats[0]; let span = first_pat.span; span_err!(cx.tcx.sess, span, E0162, "irrefutable if-let pattern"); printed_if_let_err = true; } }, hir::MatchSource::WhileLetDesugar => { // find the first arm pattern so we can use its span let &(ref first_arm_pats, _) = &arms[0]; let first_pat = &first_arm_pats[0]; let span = first_pat.span; span_err!(cx.tcx.sess, span, E0165, "irrefutable while-let pattern"); }, hir::MatchSource::ForLoopDesugar => { // this is a bug, because on `match iter.next()` we cover // `Some()` and `None`. It's impossible to have an unreachable // pattern // (see libsyntax/ext/expand.rs for the full expansion of a for loop) span_bug!(pat.span, "unreachable for-loop pattern") }, hir::MatchSource::Normal => { let mut err = struct_span_err!(cx.tcx.sess, pat.span, E0001, "unreachable pattern"); // if we had a catchall pattern, hint at that for row in &seen.0 { if pat_is_catchall(&cx.tcx.def_map.borrow(), row[0]) { span_note!(err, row[0].span, "this pattern matches any value"); } } err.emit(); }, hir::MatchSource::TryDesugar => { span_bug!(pat.span, "unreachable try pattern") }, } } Useful => (), UsefulWithWitness(_) => bug!() } if guard.is_none() { let Matrix(mut rows) = seen; rows.push(v); seen = Matrix(rows); } } } } /// Checks for common cases of "catchall" patterns that may not be intended as such. fn pat_is_catchall(dm: &DefMap, p: &Pat) -> bool { match p.node { PatKind::Binding(_, _, None) => true, PatKind::Binding(_, _, Some(ref s)) => pat_is_catchall(dm, &s), PatKind::Ref(ref s, _) => pat_is_catchall(dm, &s), PatKind::Tuple(ref v, _) => v.iter().all(|p| pat_is_catchall(dm, &p)), _ => false } } fn raw_pat(p: &Pat) -> &Pat { match p.node { PatKind::Binding(_, _, Some(ref s)) => raw_pat(&s), _ => p } } fn check_exhaustive(cx: &MatchCheckCtxt, sp: Span, matrix: &Matrix, source: hir::MatchSource) { match is_useful(cx, matrix, &[DUMMY_WILD_PAT], ConstructWitness) { UsefulWithWitness(pats) => { let witnesses = if pats.is_empty() { vec![DUMMY_WILD_PAT] } else { pats.iter().map(|w| &**w ).collect() }; match source { hir::MatchSource::ForLoopDesugar => { // `witnesses[0]` has the form `Some()`, peel off the `Some` let witness = match witnesses[0].node { PatKind::TupleStruct(_, ref pats, _) => match &pats[..] { [ref pat] => &**pat, _ => bug!(), }, _ => bug!(), }; span_err!(cx.tcx.sess, sp, E0297, "refutable pattern in `for` loop binding: \ `{}` not covered", pat_to_string(witness)); }, _ => { let pattern_strings: Vec<_> = witnesses.iter().map(|w| { pat_to_string(w) }).collect(); const LIMIT: usize = 3; let joined_patterns = match pattern_strings.len() { 0 => bug!(), 1 => format!("`{}`", pattern_strings[0]), 2...LIMIT => { let (tail, head) = pattern_strings.split_last().unwrap(); format!("`{}`", head.join("`, `") + "` and `" + tail) }, _ => { let (head, tail) = pattern_strings.split_at(LIMIT); format!("`{}` and {} more", head.join("`, `"), tail.len()) } }; span_err!(cx.tcx.sess, sp, E0004, "non-exhaustive patterns: {} not covered", joined_patterns ); }, } } NotUseful => { // This is good, wildcard pattern isn't reachable }, _ => bug!() } } fn const_val_to_expr(value: &ConstVal) -> P { let node = match value { &ConstVal::Bool(b) => ast::LitKind::Bool(b), _ => bug!() }; P(hir::Expr { id: 0, node: hir::ExprLit(P(Spanned { node: node, span: DUMMY_SP })), span: DUMMY_SP, attrs: None, }) } pub struct StaticInliner<'a, 'tcx: 'a> { pub tcx: TyCtxt<'a, 'tcx, 'tcx>, pub failed: bool, pub renaming_map: Option<&'a mut FnvHashMap<(NodeId, Span), NodeId>>, } impl<'a, 'tcx> StaticInliner<'a, 'tcx> { pub fn new<'b>(tcx: TyCtxt<'b, 'tcx, 'tcx>, renaming_map: Option<&'b mut FnvHashMap<(NodeId, Span), NodeId>>) -> StaticInliner<'b, 'tcx> { StaticInliner { tcx: tcx, failed: false, renaming_map: renaming_map } } } struct RenamingRecorder<'map> { substituted_node_id: NodeId, origin_span: Span, renaming_map: &'map mut FnvHashMap<(NodeId, Span), NodeId> } impl<'map> IdVisitingOperation for RenamingRecorder<'map> { fn visit_id(&mut self, node_id: NodeId) { let key = (node_id, self.origin_span); self.renaming_map.insert(key, self.substituted_node_id); } } impl<'a, 'tcx> Folder for StaticInliner<'a, 'tcx> { fn fold_pat(&mut self, pat: P) -> P { return match pat.node { PatKind::Path(..) | PatKind::QPath(..) => { let def = self.tcx.def_map.borrow().get(&pat.id).map(|d| d.full_def()); match def { Some(Def::AssociatedConst(did)) | Some(Def::Const(did)) => { let substs = Some(self.tcx.node_id_item_substs(pat.id).substs); if let Some((const_expr, _)) = lookup_const_by_id(self.tcx, did, substs) { match const_expr_to_pat(self.tcx, const_expr, pat.id, pat.span) { Ok(new_pat) => { if let Some(ref mut map) = self.renaming_map { // Record any renamings we do here record_renamings(const_expr, &pat, map); } new_pat } Err(def_id) => { self.failed = true; self.tcx.sess.span_err( pat.span, &format!("constants of the type `{}` \ cannot be used in patterns", self.tcx.item_path_str(def_id))); pat } } } else { self.failed = true; span_err!(self.tcx.sess, pat.span, E0158, "statics cannot be referenced in patterns"); pat } } _ => noop_fold_pat(pat, self) } } _ => noop_fold_pat(pat, self) }; fn record_renamings(const_expr: &hir::Expr, substituted_pat: &hir::Pat, renaming_map: &mut FnvHashMap<(NodeId, Span), NodeId>) { let mut renaming_recorder = RenamingRecorder { substituted_node_id: substituted_pat.id, origin_span: substituted_pat.span, renaming_map: renaming_map, }; let mut id_visitor = IdVisitor::new(&mut renaming_recorder); id_visitor.visit_expr(const_expr); } } } /// Constructs a partial witness for a pattern given a list of /// patterns expanded by the specialization step. /// /// When a pattern P is discovered to be useful, this function is used bottom-up /// to reconstruct a complete witness, e.g. a pattern P' that covers a subset /// of values, V, where each value in that set is not covered by any previously /// used patterns and is covered by the pattern P'. Examples: /// /// left_ty: tuple of 3 elements /// pats: [10, 20, _] => (10, 20, _) /// /// left_ty: struct X { a: (bool, &'static str), b: usize} /// pats: [(false, "foo"), 42] => X { a: (false, "foo"), b: 42 } fn construct_witness<'a,'tcx>(cx: &MatchCheckCtxt<'a,'tcx>, ctor: &Constructor, pats: Vec<&Pat>, left_ty: Ty<'tcx>) -> P { let pats_len = pats.len(); let mut pats = pats.into_iter().map(|p| P((*p).clone())); let pat = match left_ty.sty { ty::TyTuple(..) => PatKind::Tuple(pats.collect(), None), ty::TyEnum(adt, _) | ty::TyStruct(adt, _) => { let v = ctor.variant_for_adt(adt); match v.kind() { VariantKind::Struct => { let field_pats: hir::HirVec<_> = v.fields.iter() .zip(pats) .filter(|&(_, ref pat)| pat.node != PatKind::Wild) .map(|(field, pat)| Spanned { span: DUMMY_SP, node: hir::FieldPat { name: field.name, pat: pat, is_shorthand: false, } }).collect(); let has_more_fields = field_pats.len() < pats_len; PatKind::Struct(def_to_path(cx.tcx, v.did), field_pats, has_more_fields) } VariantKind::Tuple => { PatKind::TupleStruct(def_to_path(cx.tcx, v.did), pats.collect(), None) } VariantKind::Unit => { PatKind::Path(def_to_path(cx.tcx, v.did)) } } } ty::TyRef(_, ty::TypeAndMut { ty, mutbl }) => { match ty.sty { ty::TyArray(_, n) => match ctor { &Single => { assert_eq!(pats_len, n); PatKind::Vec(pats.collect(), None, hir::HirVec::new()) }, _ => bug!() }, ty::TySlice(_) => match ctor { &Slice(n) => { assert_eq!(pats_len, n); PatKind::Vec(pats.collect(), None, hir::HirVec::new()) }, _ => bug!() }, ty::TyStr => PatKind::Wild, _ => { assert_eq!(pats_len, 1); PatKind::Ref(pats.nth(0).unwrap(), mutbl) } } } ty::TyArray(_, len) => { assert_eq!(pats_len, len); PatKind::Vec(pats.collect(), None, hir::HirVec::new()) } _ => { match *ctor { ConstantValue(ref v) => PatKind::Lit(const_val_to_expr(v)), _ => PatKind::Wild, } } }; P(hir::Pat { id: 0, node: pat, span: DUMMY_SP }) } impl Constructor { fn variant_for_adt<'tcx, 'container, 'a>(&self, adt: &'a ty::AdtDefData<'tcx, 'container>) -> &'a VariantDefData<'tcx, 'container> { match self { &Variant(vid) => adt.variant_with_id(vid), _ => adt.struct_variant() } } } fn missing_constructors(cx: &MatchCheckCtxt, &Matrix(ref rows): &Matrix, left_ty: Ty, max_slice_length: usize) -> Vec { let used_constructors: Vec = rows.iter() .flat_map(|row| pat_constructors(cx, row[0], left_ty, max_slice_length)) .collect(); all_constructors(cx, left_ty, max_slice_length) .into_iter() .filter(|c| !used_constructors.contains(c)) .collect() } /// This determines the set of all possible constructors of a pattern matching /// values of type `left_ty`. For vectors, this would normally be an infinite set /// but is instead bounded by the maximum fixed length of slice patterns in /// the column of patterns being analyzed. fn all_constructors(_cx: &MatchCheckCtxt, left_ty: Ty, max_slice_length: usize) -> Vec { match left_ty.sty { ty::TyBool => [true, false].iter().map(|b| ConstantValue(ConstVal::Bool(*b))).collect(), ty::TyRef(_, ty::TypeAndMut { ty, .. }) => match ty.sty { ty::TySlice(_) => (0..max_slice_length+1).map(|length| Slice(length)).collect(), _ => vec![Single] }, ty::TyEnum(def, _) => def.variants.iter().map(|v| Variant(v.did)).collect(), _ => vec![Single] } } // Algorithm from http://moscova.inria.fr/~maranget/papers/warn/index.html // // Whether a vector `v` of patterns is 'useful' in relation to a set of such // vectors `m` is defined as there being a set of inputs that will match `v` // but not any of the sets in `m`. // // This is used both for reachability checking (if a pattern isn't useful in // relation to preceding patterns, it is not reachable) and exhaustiveness // checking (if a wildcard pattern is useful in relation to a matrix, the // matrix isn't exhaustive). // Note: is_useful doesn't work on empty types, as the paper notes. // So it assumes that v is non-empty. fn is_useful(cx: &MatchCheckCtxt, matrix: &Matrix, v: &[&Pat], witness: WitnessPreference) -> Usefulness { let &Matrix(ref rows) = matrix; debug!("{:?}", matrix); if rows.is_empty() { return match witness { ConstructWitness => UsefulWithWitness(vec!()), LeaveOutWitness => Useful }; } if rows[0].is_empty() { return NotUseful; } assert!(rows.iter().all(|r| r.len() == v.len())); let real_pat = match rows.iter().find(|r| (*r)[0].id != DUMMY_NODE_ID) { Some(r) => raw_pat(r[0]), None if v.is_empty() => return NotUseful, None => v[0] }; let left_ty = if real_pat.id == DUMMY_NODE_ID { cx.tcx.mk_nil() } else { let left_ty = cx.tcx.pat_ty(&real_pat); match real_pat.node { PatKind::Binding(hir::BindByRef(..), _, _) => { left_ty.builtin_deref(false, NoPreference).unwrap().ty } _ => left_ty, } }; let max_slice_length = rows.iter().filter_map(|row| match row[0].node { PatKind::Vec(ref before, _, ref after) => Some(before.len() + after.len()), _ => None }).max().map_or(0, |v| v + 1); let constructors = pat_constructors(cx, v[0], left_ty, max_slice_length); if constructors.is_empty() { let constructors = missing_constructors(cx, matrix, left_ty, max_slice_length); if constructors.is_empty() { all_constructors(cx, left_ty, max_slice_length).into_iter().map(|c| { match is_useful_specialized(cx, matrix, v, c.clone(), left_ty, witness) { UsefulWithWitness(pats) => UsefulWithWitness({ let arity = constructor_arity(cx, &c, left_ty); let mut result = { let pat_slice = &pats[..]; let subpats: Vec<_> = (0..arity).map(|i| { pat_slice.get(i).map_or(DUMMY_WILD_PAT, |p| &**p) }).collect(); vec![construct_witness(cx, &c, subpats, left_ty)] }; result.extend(pats.into_iter().skip(arity)); result }), result => result } }).find(|result| result != &NotUseful).unwrap_or(NotUseful) } else { let matrix = rows.iter().filter_map(|r| { match raw_pat(r[0]).node { PatKind::Binding(..) | PatKind::Wild => Some(r[1..].to_vec()), _ => None, } }).collect(); match is_useful(cx, &matrix, &v[1..], witness) { UsefulWithWitness(pats) => { let mut new_pats: Vec<_> = constructors.into_iter().map(|constructor| { let arity = constructor_arity(cx, &constructor, left_ty); let wild_pats = vec![DUMMY_WILD_PAT; arity]; construct_witness(cx, &constructor, wild_pats, left_ty) }).collect(); new_pats.extend(pats); UsefulWithWitness(new_pats) }, result => result } } } else { constructors.into_iter().map(|c| is_useful_specialized(cx, matrix, v, c.clone(), left_ty, witness) ).find(|result| result != &NotUseful).unwrap_or(NotUseful) } } fn is_useful_specialized(cx: &MatchCheckCtxt, &Matrix(ref m): &Matrix, v: &[&Pat], ctor: Constructor, lty: Ty, witness: WitnessPreference) -> Usefulness { let arity = constructor_arity(cx, &ctor, lty); let matrix = Matrix(m.iter().filter_map(|r| { specialize(cx, &r[..], &ctor, 0, arity) }).collect()); match specialize(cx, v, &ctor, 0, arity) { Some(v) => is_useful(cx, &matrix, &v[..], witness), None => NotUseful } } /// Determines the constructors that the given pattern can be specialized to. /// /// In most cases, there's only one constructor that a specific pattern /// represents, such as a specific enum variant or a specific literal value. /// Slice patterns, however, can match slices of different lengths. For instance, /// `[a, b, ..tail]` can match a slice of length 2, 3, 4 and so on. /// /// On the other hand, a wild pattern and an identifier pattern cannot be /// specialized in any way. fn pat_constructors(cx: &MatchCheckCtxt, p: &Pat, left_ty: Ty, max_slice_length: usize) -> Vec { let pat = raw_pat(p); match pat.node { PatKind::Struct(..) | PatKind::TupleStruct(..) | PatKind::Path(..) => match cx.tcx.def_map.borrow().get(&pat.id).unwrap().full_def() { Def::Const(..) | Def::AssociatedConst(..) => span_bug!(pat.span, "const pattern should've \ been rewritten"), Def::Struct(..) | Def::TyAlias(..) => vec![Single], Def::Variant(_, id) => vec![Variant(id)], def => span_bug!(pat.span, "pat_constructors: unexpected \ definition {:?}", def), }, PatKind::QPath(..) => span_bug!(pat.span, "const pattern should've been rewritten"), PatKind::Lit(ref expr) => vec![ConstantValue(eval_const_expr(cx.tcx, &expr))], PatKind::Range(ref lo, ref hi) => vec![ConstantRange(eval_const_expr(cx.tcx, &lo), eval_const_expr(cx.tcx, &hi))], PatKind::Vec(ref before, ref slice, ref after) => match left_ty.sty { ty::TyArray(_, _) => vec![Single], _ => if slice.is_some() { (before.len() + after.len()..max_slice_length+1) .map(|length| Slice(length)) .collect() } else { vec![Slice(before.len() + after.len())] } }, PatKind::Box(..) | PatKind::Tuple(..) | PatKind::Ref(..) => vec![Single], PatKind::Binding(..) | PatKind::Wild => vec![], } } /// This computes the arity of a constructor. The arity of a constructor /// is how many subpattern patterns of that constructor should be expanded to. /// /// For instance, a tuple pattern (_, 42, Some([])) has the arity of 3. /// A struct pattern's arity is the number of fields it contains, etc. pub fn constructor_arity(_cx: &MatchCheckCtxt, ctor: &Constructor, ty: Ty) -> usize { match ty.sty { ty::TyTuple(ref fs) => fs.len(), ty::TyBox(_) => 1, ty::TyRef(_, ty::TypeAndMut { ty, .. }) => match ty.sty { ty::TySlice(_) => match *ctor { Slice(length) => length, ConstantValue(_) => 0, _ => bug!() }, ty::TyStr => 0, _ => 1 }, ty::TyEnum(adt, _) | ty::TyStruct(adt, _) => { ctor.variant_for_adt(adt).fields.len() } ty::TyArray(_, n) => n, _ => 0 } } fn range_covered_by_constructor(ctor: &Constructor, from: &ConstVal, to: &ConstVal) -> Option { let (c_from, c_to) = match *ctor { ConstantValue(ref value) => (value, value), ConstantRange(ref from, ref to) => (from, to), Single => return Some(true), _ => bug!() }; let cmp_from = compare_const_vals(c_from, from); let cmp_to = compare_const_vals(c_to, to); match (cmp_from, cmp_to) { (Some(cmp_from), Some(cmp_to)) => { Some(cmp_from != Ordering::Less && cmp_to != Ordering::Greater) } _ => None } } /// This is the main specialization step. It expands the first pattern in the given row /// into `arity` patterns based on the constructor. For most patterns, the step is trivial, /// for instance tuple patterns are flattened and box patterns expand into their inner pattern. /// /// OTOH, slice patterns with a subslice pattern (..tail) can be expanded into multiple /// different patterns. /// Structure patterns with a partial wild pattern (Foo { a: 42, .. }) have their missing /// fields filled with wild patterns. pub fn specialize<'a>(cx: &MatchCheckCtxt, r: &[&'a Pat], constructor: &Constructor, col: usize, arity: usize) -> Option> { let &Pat { id: pat_id, ref node, span: pat_span } = raw_pat(r[col]); let head: Option> = match *node { PatKind::Binding(..) | PatKind::Wild => Some(vec![DUMMY_WILD_PAT; arity]), PatKind::Path(..) => { let def = cx.tcx.def_map.borrow().get(&pat_id).unwrap().full_def(); match def { Def::Const(..) | Def::AssociatedConst(..) => span_bug!(pat_span, "const pattern should've \ been rewritten"), Def::Variant(_, id) if *constructor != Variant(id) => None, Def::Variant(..) | Def::Struct(..) => Some(Vec::new()), _ => span_bug!(pat_span, "specialize: unexpected \ definition {:?}", def), } } PatKind::TupleStruct(_, ref args, ddpos) => { let def = cx.tcx.def_map.borrow().get(&pat_id).unwrap().full_def(); match def { Def::Const(..) | Def::AssociatedConst(..) => span_bug!(pat_span, "const pattern should've \ been rewritten"), Def::Variant(_, id) if *constructor != Variant(id) => None, Def::Variant(..) | Def::Struct(..) => { match ddpos { Some(ddpos) => { let mut pats: Vec<_> = args[..ddpos].iter().map(|p| &**p).collect(); pats.extend(repeat(DUMMY_WILD_PAT).take(arity - args.len())); pats.extend(args[ddpos..].iter().map(|p| &**p)); Some(pats) } None => Some(args.iter().map(|p| &**p).collect()) } } _ => None } } PatKind::QPath(_, _) => { span_bug!(pat_span, "const pattern should've been rewritten") } PatKind::Struct(_, ref pattern_fields, _) => { let def = cx.tcx.def_map.borrow().get(&pat_id).unwrap().full_def(); let adt = cx.tcx.node_id_to_type(pat_id).ty_adt_def().unwrap(); let variant = constructor.variant_for_adt(adt); let def_variant = adt.variant_of_def(def); if variant.did == def_variant.did { Some(variant.fields.iter().map(|sf| { match pattern_fields.iter().find(|f| f.node.name == sf.name) { Some(ref f) => &*f.node.pat, _ => DUMMY_WILD_PAT } }).collect()) } else { None } } PatKind::Tuple(ref args, Some(ddpos)) => { let mut pats: Vec<_> = args[..ddpos].iter().map(|p| &**p).collect(); pats.extend(repeat(DUMMY_WILD_PAT).take(arity - args.len())); pats.extend(args[ddpos..].iter().map(|p| &**p)); Some(pats) } PatKind::Tuple(ref args, None) => Some(args.iter().map(|p| &**p).collect()), PatKind::Box(ref inner) | PatKind::Ref(ref inner, _) => Some(vec![&**inner]), PatKind::Lit(ref expr) => { let expr_value = eval_const_expr(cx.tcx, &expr); match range_covered_by_constructor(constructor, &expr_value, &expr_value) { Some(true) => Some(vec![]), Some(false) => None, None => { span_err!(cx.tcx.sess, pat_span, E0298, "mismatched types between arms"); None } } } PatKind::Range(ref from, ref to) => { let from_value = eval_const_expr(cx.tcx, &from); let to_value = eval_const_expr(cx.tcx, &to); match range_covered_by_constructor(constructor, &from_value, &to_value) { Some(true) => Some(vec![]), Some(false) => None, None => { span_err!(cx.tcx.sess, pat_span, E0299, "mismatched types between arms"); None } } } PatKind::Vec(ref before, ref slice, ref after) => { match *constructor { // Fixed-length vectors. Single => { let mut pats: Vec<&Pat> = before.iter().map(|p| &**p).collect(); pats.extend(repeat(DUMMY_WILD_PAT).take(arity - before.len() - after.len())); pats.extend(after.iter().map(|p| &**p)); Some(pats) }, Slice(length) if before.len() + after.len() <= length && slice.is_some() => { let mut pats: Vec<&Pat> = before.iter().map(|p| &**p).collect(); pats.extend(repeat(DUMMY_WILD_PAT).take(arity - before.len() - after.len())); pats.extend(after.iter().map(|p| &**p)); Some(pats) }, Slice(length) if before.len() + after.len() == length => { let mut pats: Vec<&Pat> = before.iter().map(|p| &**p).collect(); pats.extend(after.iter().map(|p| &**p)); Some(pats) }, SliceWithSubslice(prefix, suffix) if before.len() == prefix && after.len() == suffix && slice.is_some() => { let mut pats: Vec<&Pat> = before.iter().map(|p| &**p).collect(); pats.extend(after.iter().map(|p| &**p)); Some(pats) } _ => None } } }; head.map(|mut head| { head.extend_from_slice(&r[..col]); head.extend_from_slice(&r[col + 1..]); head }) } fn check_local(cx: &mut MatchCheckCtxt, loc: &hir::Local) { intravisit::walk_local(cx, loc); let pat = StaticInliner::new(cx.tcx, None).fold_pat(loc.pat.clone()); check_irrefutable(cx, &pat, false); // Check legality of move bindings and `@` patterns. check_legality_of_move_bindings(cx, false, slice::ref_slice(&loc.pat)); check_legality_of_bindings_in_at_patterns(cx, &loc.pat); } fn check_fn(cx: &mut MatchCheckCtxt, kind: FnKind, decl: &hir::FnDecl, body: &hir::Block, sp: Span, fn_id: NodeId) { match kind { FnKind::Closure(_) => {} _ => cx.param_env = ParameterEnvironment::for_item(cx.tcx, fn_id), } intravisit::walk_fn(cx, kind, decl, body, sp); for input in &decl.inputs { check_irrefutable(cx, &input.pat, true); check_legality_of_move_bindings(cx, false, slice::ref_slice(&input.pat)); check_legality_of_bindings_in_at_patterns(cx, &input.pat); } } fn check_irrefutable(cx: &MatchCheckCtxt, pat: &Pat, is_fn_arg: bool) { let origin = if is_fn_arg { "function argument" } else { "local binding" }; is_refutable(cx, pat, |uncovered_pat| { span_err!(cx.tcx.sess, pat.span, E0005, "refutable pattern in {}: `{}` not covered", origin, pat_to_string(uncovered_pat), ); }); } fn is_refutable(cx: &MatchCheckCtxt, pat: &Pat, refutable: F) -> Option where F: FnOnce(&Pat) -> A, { let pats = Matrix(vec!(vec!(pat))); match is_useful(cx, &pats, &[DUMMY_WILD_PAT], ConstructWitness) { UsefulWithWitness(pats) => Some(refutable(&pats[0])), NotUseful => None, Useful => bug!() } } // Legality of move bindings checking fn check_legality_of_move_bindings(cx: &MatchCheckCtxt, has_guard: bool, pats: &[P]) { let mut by_ref_span = None; for pat in pats { pat_bindings(&pat, |bm, _, span, _path| { if let hir::BindByRef(..) = bm { by_ref_span = Some(span); } }) } let check_move = |p: &Pat, sub: Option<&Pat>| { // check legality of moving out of the enum // x @ Foo(..) is legal, but x @ Foo(y) isn't. if sub.map_or(false, |p| pat_contains_bindings(&p)) { span_err!(cx.tcx.sess, p.span, E0007, "cannot bind by-move with sub-bindings"); } else if has_guard { span_err!(cx.tcx.sess, p.span, E0008, "cannot bind by-move into a pattern guard"); } else if by_ref_span.is_some() { let mut err = struct_span_err!(cx.tcx.sess, p.span, E0009, "cannot bind by-move and by-ref in the same pattern"); span_note!(&mut err, by_ref_span.unwrap(), "by-ref binding occurs here"); err.emit(); } }; for pat in pats { pat.walk(|p| { if let PatKind::Binding(hir::BindByValue(..), _, ref sub) = p.node { let pat_ty = cx.tcx.node_id_to_type(p.id); //FIXME: (@jroesch) this code should be floated up as well cx.tcx.infer_ctxt(None, Some(cx.param_env.clone()), ProjectionMode::AnyFinal).enter(|infcx| { if infcx.type_moves_by_default(pat_ty, pat.span) { check_move(p, sub.as_ref().map(|p| &**p)); } }); } true }); } } /// Ensures that a pattern guard doesn't borrow by mutable reference or /// assign. fn check_for_mutation_in_guard<'a, 'tcx>(cx: &'a MatchCheckCtxt<'a, 'tcx>, guard: &hir::Expr) { cx.tcx.infer_ctxt(None, Some(cx.param_env.clone()), ProjectionMode::AnyFinal).enter(|infcx| { let mut checker = MutationChecker { cx: cx, }; let mut visitor = ExprUseVisitor::new(&mut checker, &infcx); visitor.walk_expr(guard); }); } struct MutationChecker<'a, 'gcx: 'a> { cx: &'a MatchCheckCtxt<'a, 'gcx>, } impl<'a, 'gcx, 'tcx> Delegate<'tcx> for MutationChecker<'a, 'gcx> { fn matched_pat(&mut self, _: &Pat, _: cmt, _: euv::MatchMode) {} fn consume(&mut self, _: NodeId, _: Span, _: cmt, _: ConsumeMode) {} fn consume_pat(&mut self, _: &Pat, _: cmt, _: ConsumeMode) {} fn borrow(&mut self, _: NodeId, span: Span, _: cmt, _: Region, kind: BorrowKind, _: LoanCause) { match kind { MutBorrow => { span_err!(self.cx.tcx.sess, span, E0301, "cannot mutably borrow in a pattern guard") } ImmBorrow | UniqueImmBorrow => {} } } fn decl_without_init(&mut self, _: NodeId, _: Span) {} fn mutate(&mut self, _: NodeId, span: Span, _: cmt, mode: MutateMode) { match mode { MutateMode::JustWrite | MutateMode::WriteAndRead => { span_err!(self.cx.tcx.sess, span, E0302, "cannot assign in a pattern guard") } MutateMode::Init => {} } } } /// Forbids bindings in `@` patterns. This is necessary for memory safety, /// because of the way rvalues are handled in the borrow check. (See issue /// #14587.) fn check_legality_of_bindings_in_at_patterns(cx: &MatchCheckCtxt, pat: &Pat) { AtBindingPatternVisitor { cx: cx, bindings_allowed: true }.visit_pat(pat); } struct AtBindingPatternVisitor<'a, 'b:'a, 'tcx:'b> { cx: &'a MatchCheckCtxt<'b, 'tcx>, bindings_allowed: bool } impl<'a, 'b, 'tcx, 'v> Visitor<'v> for AtBindingPatternVisitor<'a, 'b, 'tcx> { fn visit_pat(&mut self, pat: &Pat) { match pat.node { PatKind::Binding(_, _, ref subpat) => { if !self.bindings_allowed { span_err!(self.cx.tcx.sess, pat.span, E0303, "pattern bindings are not allowed after an `@`"); } if subpat.is_some() { let bindings_were_allowed = self.bindings_allowed; self.bindings_allowed = false; intravisit::walk_pat(self, pat); self.bindings_allowed = bindings_were_allowed; } } _ => intravisit::walk_pat(self, pat), } } }